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4 5<book id="regulator-api">
6 <bookinfo>
7 <title>Voltage and current regulator API</title>
8 9 <authorgroup>
10 <author>
11 <firstname>Liam</firstname>
12 <surname>Girdwood</surname>
13 <affiliation>
14 <address>
15 <email>lrg@slimlogic.co.uk</email>
16 </address>
17 </affiliation>
18 </author>
19 <author>
20 <firstname>Mark</firstname>
21 <surname>Brown</surname>
22 <affiliation>
23 <orgname>Wolfson Microelectronics</orgname>
24 <address>
25 <email>broonie@opensource.wolfsonmicro.com</email>
26 </address>
27 </affiliation>
28 </author>
29 </authorgroup>
30 31 <copyright>
32 <year>2007-2008</year>
33 <holder>Wolfson Microelectronics</holder>
34 </copyright>
35 <copyright>
36 <year>2008</year>
37 <holder>Liam Girdwood</holder>
38 </copyright>
39 40 <legalnotice>
41 <para>
42 This documentation is free software; you can redistribute
43 it and/or modify it under the terms of the GNU General Public
44 License version 2 as published by the Free Software Foundation.
45 </para>
46 47 <para>
48 This program is distributed in the hope that it will be
49 useful, but WITHOUT ANY WARRANTY; without even the implied
50 warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
51 See the GNU General Public License for more details.
52 </para>
53 54 <para>
55 You should have received a copy of the GNU General Public
56 License along with this program; if not, write to the Free
57 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
58 MA 02111-1307 USA
59 </para>
60 61 <para>
62 For more details see the file COPYING in the source
63 distribution of Linux.
64 </para>
65 </legalnotice>
66 </bookinfo>
67 68<toc></toc>
69 70 <chapter id="intro">
71 <title>Introduction</title>
72 <para>
73 This framework is designed to provide a standard kernel
74 interface to control voltage and current regulators.
75 </para>
76 <para>
77 The intention is to allow systems to dynamically control
78 regulator power output in order to save power and prolong
79 battery life. This applies to both voltage regulators (where
80 voltage output is controllable) and current sinks (where current
81 limit is controllable).
82 </para>
83 <para>
84 Note that additional (and currently more complete) documentation
85 is available in the Linux kernel source under
86 <filename>Documentation/power/regulator</filename>.
87 </para>
88 89 <sect1 id="glossary">
90 <title>Glossary</title>
91 <para>
92 The regulator API uses a number of terms which may not be
93 familiar:
94 </para>
95 <glossary>
96 97 <glossentry>
98 <glossterm>Regulator</glossterm>
99 <glossdef>
100 <para>
101 Electronic device that supplies power to other devices. Most
102 regulators can enable and disable their output and some can also
103 control their output voltage or current.
104 </para>
105 </glossdef>
106 </glossentry>
107 108 <glossentry>
109 <glossterm>Consumer</glossterm>
110 <glossdef>
111 <para>
112 Electronic device which consumes power provided by a regulator.
113 These may either be static, requiring only a fixed supply, or
114 dynamic, requiring active management of the regulator at
115 runtime.
116 </para>
117 </glossdef>
118 </glossentry>
119 120 <glossentry>
121 <glossterm>Power Domain</glossterm>
122 <glossdef>
123 <para>
124 The electronic circuit supplied by a given regulator, including
125 the regulator and all consumer devices. The configuration of
126 the regulator is shared between all the components in the
127 circuit.
128 </para>
129 </glossdef>
130 </glossentry>
131 132 <glossentry>
133 <glossterm>Power Management Integrated Circuit</glossterm>
134 <acronym>PMIC</acronym>
135 <glossdef>
136 <para>
137 An IC which contains numerous regulators and often also other
138 subsystems. In an embedded system the primary PMIC is often
139 equivalent to a combination of the PSU and southbridge in a
140 desktop system.
141 </para>
142 </glossdef>
143 </glossentry>
144 </glossary>
145 </sect1>
146 </chapter>
147 148 <chapter id="consumer">
149 <title>Consumer driver interface</title>
150 <para>
151 This offers a similar API to the kernel clock framework.
152 Consumer drivers use <link
153 linkend='API-regulator-get'>get</link> and <link
154 linkend='API-regulator-put'>put</link> operations to acquire and
155 release regulators. Functions are
156 provided to <link linkend='API-regulator-enable'>enable</link>
157 and <link linkend='API-regulator-disable'>disable</link> the
158 reguator and to get and set the runtime parameters of the
159 regulator.
160 </para>
161 <para>
162 When requesting regulators consumers use symbolic names for their
163 supplies, such as "Vcc", which are mapped into actual regulator
164 devices by the machine interface.
165 </para>
166 <para>
167 A stub version of this API is provided when the regulator
168 framework is not in use in order to minimise the need to use
169 ifdefs.
170 </para>
171 172 <sect1 id="consumer-enable">
173 <title>Enabling and disabling</title>
174 <para>
175 The regulator API provides reference counted enabling and
176 disabling of regulators. Consumer devices use the <function><link
177 linkend='API-regulator-enable'>regulator_enable</link></function>
178 and <function><link
179 linkend='API-regulator-disable'>regulator_disable</link>
180 </function> functions to enable and disable regulators. Calls
181 to the two functions must be balanced.
182 </para>
183 <para>
184 Note that since multiple consumers may be using a regulator and
185 machine constraints may not allow the regulator to be disabled
186 there is no guarantee that calling
187 <function>regulator_disable</function> will actually cause the
188 supply provided by the regulator to be disabled. Consumer
189 drivers should assume that the regulator may be enabled at all
190 times.
191 </para>
192 </sect1>
193 194 <sect1 id="consumer-config">
195 <title>Configuration</title>
196 <para>
197 Some consumer devices may need to be able to dynamically
198 configure their supplies. For example, MMC drivers may need to
199 select the correct operating voltage for their cards. This may
200 be done while the regulator is enabled or disabled.
201 </para>
202 <para>
203 The <function><link
204 linkend='API-regulator-set-voltage'>regulator_set_voltage</link>
205 </function> and <function><link
206 linkend='API-regulator-set-current-limit'
207 >regulator_set_current_limit</link>
208 </function> functions provide the primary interface for this.
209 Both take ranges of voltages and currents, supporting drivers
210 that do not require a specific value (eg, CPU frequency scaling
211 normally permits the CPU to use a wider range of supply
212 voltages at lower frequencies but does not require that the
213 supply voltage be lowered). Where an exact value is required
214 both minimum and maximum values should be identical.
215 </para>
216 </sect1>
217 218 <sect1 id="consumer-callback">
219 <title>Callbacks</title>
220 <para>
221 Callbacks may also be <link
222 linkend='API-regulator-register-notifier'>registered</link>
223 for events such as regulation failures.
224 </para>
225 </sect1>
226 </chapter>
227 228 <chapter id="driver">
229 <title>Regulator driver interface</title>
230 <para>
231 Drivers for regulator chips <link
232 linkend='API-regulator-register'>register</link> the regulators
233 with the regulator core, providing operations structures to the
234 core. A <link
235 linkend='API-regulator-notifier-call-chain'>notifier</link> interface
236 allows error conditions to be reported to the core.
237 </para>
238 <para>
239 Registration should be triggered by explicit setup done by the
240 platform, supplying a <link
241 linkend='API-struct-regulator-init-data'>struct
242 regulator_init_data</link> for the regulator containing
243 <link linkend='machine-constraint'>constraint</link> and
244 <link linkend='machine-supply'>supply</link> information.
245 </para>
246 </chapter>
247 248 <chapter id="machine">
249 <title>Machine interface</title>
250 <para>
251 This interface provides a way to define how regulators are
252 connected to consumers on a given system and what the valid
253 operating parameters are for the system.
254 </para>
255 256 <sect1 id="machine-supply">
257 <title>Supplies</title>
258 <para>
259 Regulator supplies are specified using <link
260 linkend='API-struct-regulator-consumer-supply'>struct
261 regulator_consumer_supply</link>. This is done at
262 <link linkend='driver'>driver registration
263 time</link> as part of the machine constraints.
264 </para>
265 </sect1>
266 267 <sect1 id="machine-constraint">
268 <title>Constraints</title>
269 <para>
270 As well as defining the connections the machine interface
271 also provides constraints defining the operations that
272 clients are allowed to perform and the parameters that may be
273 set. This is required since generally regulator devices will
274 offer more flexibility than it is safe to use on a given
275 system, for example supporting higher supply voltages than the
276 consumers are rated for.
277 </para>
278 <para>
279 This is done at <link linkend='driver'>driver
280 registration time</link> by providing a <link
281 linkend='API-struct-regulation-constraints'>struct
282 regulation_constraints</link>.
283 </para>
284 <para>
285 The constraints may also specify an initial configuration for the
286 regulator in the constraints, which is particularly useful for
287 use with static consumers.
288 </para>
289 </sect1>
290 </chapter>
291 292 <chapter id="api">
293 <title>API reference</title>
294 <para>
295 Due to limitations of the kernel documentation framework and the
296 existing layout of the source code the entire regulator API is
297 documented here.
298 </para>
299!Iinclude/linux/regulator/consumer.h
300!Iinclude/linux/regulator/machine.h
301!Iinclude/linux/regulator/driver.h
302!Edrivers/regulator/core.c
303 </chapter>
304</book>
305